1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copier, a facsimile machine, and a multifunctional system that performs cleaning of a member by using a motor for rotating a rotation shaft to move a movable body.
2. Description of Related Art
Image forming apparatuses are sometimes provided with a mechanism that uses a motor or the like to automatically remove stain caused by dust of toner, external additives of toner (e.g., silica), and the like. For example, in an image forming apparatus in which a photoconductive drum is charged by corona discharge from a wire, electrostatic force generated by a voltage applied to the wire may sometimes cause a substance such as dust of silica to adhere to the wire, and this substance adhered to the wire is automatically removed by use of a motor and the like.
An example of an image forming apparatus in which a wire is cleaned by use of a motor and the like is disclosed in JP-A-H01-116659. Specifically, JP-A-H01-116659 discloses a wire cleaning unit for use in a corona discharge device incorporated in an image forming apparatus that performs image recording on recording paper, the wire cleaning unit including: cleaning means for cleaning a charging wire of the corona discharge device; a motor for moving this cleaning means; overcurrent detecting means for detecting an overcurrent flowing through the motor; time counting means that starts counting time substantially at the same time the cleaning means starts moving; failure detecting means for judging whether or not the cleaning device has stopped halfway when an overcurrent is detected by the overcurrent detecting means and according to counted time; and control means that, in response to detection of failure, permits image recording to be performed on recording paper so sized that the image recording can be performed thereon without being negatively affected by the failure and prohibits image recording from being performed on recording paper so sized that the image recording, if performed thereon, will be negatively affected by the failure. This structure helps prevent abnormality from occurring in a recorded image due to an abnormal stop of cleaning operation.
Here, in some of the cases where a wire of a charging device and a glass portion of a laser unit functioning as an exposure device are automatically cleaned by using, for example, a motor, cleaning is performed by driving the motor for a given time to move a movable body provided with a cleaning member.
However, the amount of load on the motor varies depending on, for example, how dirty a target to be cleaned is, and time necessary for the cleaning member to be moved over a predetermined distance also varies with the amount of load. Thus, if the motor is driven only for the given time, the movable body sometimes cannot reach a terminal position, and thus cleaning is stopped halfway, which is inconvenient.
Also, there is a case where a stopper or the like is provided at the end point of the travel of the movable body and cleaning is judged to have been completed when an overcurrent is detected flowing through the motor. Inconveniently, however, an overcurrent is sometimes detected before cleaning is completed, due to noise from noise sources incorporated in the image forming apparatus such as a charging unit and a transfer unit that emit high voltages, and noise from printing paper that is charged with electrostatic.
Incidentally, the invention disclosed in JP-A-H01-116659 only attempts to prevent generation of an abnormal recorded image by selecting printing paper sized such that image formation thereon will not be negatively affected by an abnormal stop of the cleaning means according to how long the cleaning means has moved, that is, the time counted from the start of a travel of the cleaning member to detection of an overcurrent, and according to how fast the cleaning means has moved (see lines 1 to 3 of the left column in page 2); detection errors caused by noise or the like are not considered in the invention. That is, in the invention disclosed in JP-A-H01-116659, since the rotation direction of a motor is reversed as soon as an overcurrent is detected, it is impossible to correctly judge whether the overcurrent has occurred because of a large load, noise, or a failure, and it is also impossible to correctly judge whether or not the motor should be permitted to continue rotating.